1. Field of the Invention
The present invention relates to a broadcast transport stream (hereinafter, referred to as a TS) distribution system which packetizes TSs of broadcast program contents and distributes them via a communication line through an Internet Protocol (IP) network.
2. Description of the Related Art
Recently, a video on demand (hereinafter, referred to as a VOD) service has become widely available through IP broadcasting by using a communication line through the IP network, which has resulted from the widespread use of broadband. Some of such services to distribute TS packets, which have been used in terrestrial digital broadcasting, etc., have begun to be offered by the use of such communication lines. In such a service, there is a need to suppress transmission rates as much as possible. Therefore, a technique which reduces the total amount of transmission data and intends to decrease the transmission rates by discarding unnecessary packets is disclosed (refer to, e.g., Jpn. Pat. Appln. No. 2006-151527).
Meanwhile, a user terminal device to receive TS packets which are IP-packetized by using the communication line obtains data by securing a buffer area so as to absorb the delay on the communication line and the irregularity (fluctuation) of data arrival times, and obtains data. However, the size of the buffer area is set on the premise that a distribution apparatus transmits the IP-packetized TS packets at a constant rate. Therefore, if subtle deviations in transmission rates of the distribution apparatus occur, and if the user terminal device continues to receive the IP-packetized TS packets for a long time, the ‘deviations’ results in accumulation, and there is the possibility of an occurrence of underflow or overflow of the buffer area. In the case of an underflow, the user terminal device generates blackout on a presentation, and in the case of an overflow, the overflow results in an increase in the delay because the size of the buffer area is large, or an occurrence of a video jump so as to correct the delay.
As regards such a problem, compensation by notifying information for adjusting the transmission rates to the distribution apparatus from the user terminal device in the use of an interactive protocol such as a real-time transport protocol control protocol (RTCP) is a possible approach. However, in broadcast-distribution of broadcast content, responding to requests from all user terminal devices poses a large load on a server on a distribution-side, so that it is not a realistic response to respond to a huge number of users.
As given above, in the case of distribution of the broadcast TSs by converting them into the IP packets, subtle deviations in the transmission rates are accumulated in the buffer area on the user terminal device-side, and this results in a risk of underflow or overflow in the buffer.